In order to make the injection molding go smoothly, the quality of the plastic products is guaranteed. Before the injection molding, the inspection and pre-heat treatment of the raw materials must be done. The following plastic mold manufacturers will introduce how to carry out the inspection and pre-heat treatment of the raw materials.
Inspection and preheating of raw materials
The appearance and process performance of the raw materials should be checked before molding. The contents include color, particle size and uniformity, fluidity (melt index, viscosity), heat stability, shrinkage, moisture content and the like. Some products require no color or transparency. The desired colorant should be added to the raw material before molding. If the color masterbatch is added to the raw material, the effect is better.
For water-absorbent plastics (such as polysulfone, polymethyl, etc.) must be dried before molding. Otherwise, defects such as streaks, silver filaments and air bubbles will appear on the surface of the plastic product, and even the polymer will be degraded during molding. Seriously affect the quality of the product. For plastics that are not easy to absorb water (such as polyethylene, polypropylene, etc.), as long as they are packaged, transported, and stored well, they generally do not need to be dried. Polystyrene and ABS plastics are also often dried.
The method of drying treatment should be selected according to the properties of plastics and the amount of production. The plastics used for small batch production are mostly dried by hot air circulating drying oven and infrared heating oven. For mass production of plastics, vacuum drying or vacuum should be used. Dry, good effect, short time. The drying effect has a great relationship with temperature and time. Generally speaking, the temperature is high, the time is long, and the drying effect is good, but the temperature should not be too high, and the time should not be too long. If the temperature exceeds the glass transition temperature or melting point, the plastic will agglomerate. It is difficult to add during molding. For plastics with poor thermal stability, it will cause discoloration, degradation, and the plastic after drying should be used immediately. Otherwise, it should be properly stored to prevent further moisture.